The present invention relates to a jerk limit control system for limiting sudden changes in braking force of a railway vehicle, in order to eliminate passenger discomfort, and more particularly to such systems where the jerk limiting function is monitored to detect a malfunction.
One such known system is explained with reference to FIGS. 10 and 11 of the drawings. A brake controller 1 generates an electric brake command signal E1, which is connected to a jerk limit control circuit 2. The output of circuit 2 provides a jerk limit signal E2, which can be seen from the graph of FIG. 11, to exhibit a gradual change in response to instantaneous changes in the brake command signal E1. Jerk limit signal E2 is connected to the primary brake system 3A to control normal brake operation, the changes in braking intensity being without passenger discomfort due to the jerk limiting function.
In addition, the known arrangement includes a difference detector circuit 4, which compares signals E1 and E2, and outputs a malfunction signal E4 anytime a difference exists between signals E1 and E2. Malfunction signal E4 actuates an off delay-type timer, which suppresses the malfunction signal for a predetermined time period (t) following a change in the brake command signal E1 relative to signal E2. Time period (t) is set according to the delay imposed by jerk limit signal E2, in order to prevent a false malfunction indication from being generated by the signal level difference between E1 and E2 during the jerk limiting operation. Timer circuit 5 outputs a signal E5 following time delay (t) to operate a secondary brake system 3B, in the event primary brake system 3A is inoperative due to a malfunction of jerk limit control circuit 2.
As an alternative to the secondary brake system 3B, a redundant jerk limit control circuit 2' may be employed to control the primary brake system in the event a malfunction occurs in the primary jerk limit control system 2. This alternative arrangement is shown by the dotted lines in FIG. 10. In such an arrangement, the secondary brake system 3B may be eliminated, with the output signal E5 of timer circuit 5 initiating operation of redundant jerk limit control circuit 2'.
Either one of these known arrangements serves the purpose of ridding the passengers' feeling of unpleasantness due to sudden changes in braking force resulting from the high degree of response of the primary brake system 3A to the brake command signal E1.
As shown in FIG. 11b, however, a problem in these known systems arises when brake command signal E1 is repeatedly changed at relatively close intervals, i e., intervals of time shorter than the predetermined time period (t) established by timer circuit 5. These repeated changes in brake command signal E1 being at such close intervals, signal E2 does not have sufficient time to rise or fall to the level of signal E1, and difference detector 4 continuously outputs malfunction signal E4, as represented by a logical "0" state in the graph of FIG. 11b, beyond time period (t). Accordingly, the timer circuit output signal E5 is generated, not in response to a difference between signals E1 and E2 resulting from a malfunction, but instead, from a difference due to repeated brake command changes at relatively short intervals. Thus, a false malfunction is indicated and the secondary brake system 3B, or the redundant jerk control circuit 2', is unnecessarily activated.
The foregoing problem can be overcome by increasing time period (t), but this delays recognition of an actual malfunction of the jerk control circuit 2 and is therefore unsatisfactory from a safety standpoint.